Method and apparatus for an optimized fuel control based on outlet oxygen signal to reduce vehicle missions

ABSTRACT

A control system and method for optimizing fuel control in an internal combustion engine utilizes a signal from an oxygen sensor disposed in an exhaust downstream of a catalytic converter. An air/fuel mixture introduced into the engine is compensated based on the signal exceeding predetermined enabling thresholds. The predetermined rich or lean condition enable threshold represents an oxygen content so less or greater than desired that the normal closed loop control including regular secondary fuel trim is not sufficient enough to bring the outlet oxygen sensor signal back to the desired window quickly. A reduced or increased amount of fuel is introduced into the engine based on the signal exceeding the predetermined rich or lean enable threshold respectively.

FIELD OF THE INVENTION

The present invention relates to fuel control systems for gasoline vehicles, and more particularly to engine fuel control systems including an oxygen sensor that is located downstream from a three-way catalytic converter.

BACKGROUND OF THE INVENTION

Three-way catalytic converters reduce exhaust gas emissions in vehicles using an internal combustion engine. The catalytic converter includes a substrate with a coating of catalyst materials that stimulate the oxidation of hydrocarbon and carbon monoxide molecules, and the reduction of nitrogen oxides, in the vehicle exhaust gas. The catalysts operate optimally when the temperature of the catalysts is above a minimum level and when the air/fuel ratio is stoichiometric. Stoichiometry is defined as an ideal air/fuel ratio, which is 14.7 to 1 for gasoline.

Fuel delivery is managed by an engine control system using either open loop or closed loop feedback control. Open loop control is typically initiated during specific operating conditions such as start up, cold engine operation, heavy load conditions, wide open throttle, and intrusive diagnostic events, etc.

An engine control system typically employs closed loop control to maintain the air/fuel mixture at or close to the ideal stoichiometric air/fuel ratio. Closed loop fuel control commands a desired fuel delivery based on the oxygen content in the exhaust. The oxygen level in the exhaust is determined by oxygen sensors that are located both upstream and downstream from the catalytic converter. A three-way catalytic converter and the upstream and downstream oxygen sensors are used in gasoline vehicles for emission reduction. The upstream (inlet oxygen sensor) and downstream oxygen sensor (outlet oxygen sensor) are also used for catalytic converter efficiency monitoring.

Primary closed loop fuel control using an oxygen sensor upstream from a catalytic converter has been widely used, driven by fuel economy and emission reduction. The fundamental idea is to try to maintain catalytic converter inlet oxygen sensor signals toggling around a reference voltage to provide engine combustion at or close to stoichiometric air/fuel ratios.

Secondary fuel trim using an oxygen sensor after a catalytic converter is also widely used and is mainly driven by trying to meet increasingly stringent emission regulations. The outlet oxygen sensor signal correlates to air/fuel ratios or rich/lean conditions in the catalyst-out gas flow. A three-way catalytic converter has the capacity to store or release oxygen, and thus can maintain good catalyst efficiency despite small or short duration fueling errors from the ideal stoichiometric air/fuel ratio. However, large or long duration fueling errors from stoichiometric, will make emissions break through the catalytic converter, which can be observed by the outlet oxygen sensor signals going to very low or very high voltages. Secondary fuel trim works to maintain the catalytic converter outlet oxygen sensor signal within a window identified as providing optimal catalytic converter efficiency.

Given the primary closed loop fuel control and secondary fuel trim as designed, there still exists several normal maneuvers as well as intrusive diagnostic tests that could saturate the converter and lead to increased emissions break through. The intrusive diagnostic tests for performance monitoring of the catalytic converters, outlet oxygen sensors and secondary air injection are a few examples of diagnostic tests that can leave the converter in a lower efficiency state. The invention is to minimize these negative impacts and reduce catalyst-out emissions by quickly taking fuel control actions that force outlet oxygen signals back toward the normal or desired zone to get optimum catalyst efficiency. The methodology is to add four new thresholds in addition to the existing target window for the outlet oxygen sensor signal to further optimize engine fuel control strategy.

SUMMARY OF THE INVENTION

A control system and method for optimizing fuel control in an internal combustion engine utilizes a signal from an oxygen sensor disposed in an exhaust downstream of a catalytic converter. Control determines whether the signal exceeds predetermined thresholds. An air/fuel mixture introduced into the engine is compensated based on the signal exceeding the predetermined thresholds.

To enable rich fuel compensation for a lean downstream condition, control compares the downstream oxygen sensor signal to a predetermined lean condition enable threshold that represents an oxygen content so greater than desired that the normal closed loop control including regular secondary fuel trim is not sufficient enough to bring the outlet oxygen sensor signal back to the desired window quickly. An increased amount of fuel is introduced into the engine based on the signal exceeding (dropping lower than) the predetermined lean condition enable threshold. Similarly, to enable lean fuel compensation for a rich downstream condition, control compares the signal to a predetermined rich condition enable threshold that represents an oxygen content so less than desired that the normal closed loop control including regular secondary fuel trim is not sufficient enough to bring the outlet oxygen sensor signal back to the desired window quickly. A reduced amount of fuel is introduced into the engine based on the signal exceeding the predetermined rich condition enable threshold.

Once rich fuel compensation for a lean downstream condition has been enabled, control compares the signal to a predetermined lean condition disable threshold that represents an oxygen content greater than a desired level, but appropriate for providing normal closed loop fueling once again. Fuel delivery is returned to normal closed loop operation based on the signal satisfying or rising above the lean condition disable threshold. Similarly, once lean fuel compensation for a rich downstream condition has been enabled, control compares the signal to a predetermined rich condition disable threshold that represents an oxygen content less than a desired level, but appropriate for providing normal closed loop fueling once again. Fuel delivery is returned to normal closed loop operation based on the signal satisfying or dropping lower than the rich condition disable threshold.

According to other features, this control is only used while meeting closed loop conditions with normally functioning oxygen sensors and while not in an intrusive diagnostic test or any other open loop fuel.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an engine control system according to the present invention for a vehicle;

FIG. 2 illustrates outlet oxygen sensor thresholds according to the present invention;

FIG. 3 is a flow diagram illustrating steps for optimizing fuel control; and

FIG. 4 is a flow diagram illustrating steps for implementing the fuel correction of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Referring to FIG. 1, an exemplary engine control system 8 is shown. A throttle 10 and a fuel system 12 control the air/fuel mixture that is delivered to an engine 14 through an intake 16. An ignition system 18 ignites the fuel and air mixture in the engine 14. Exhaust gas that is created by the combustion of the air/fuel mixture is expelled through an exhaust manifold 20. A catalytic converter 22 receives the exhaust gas from the exhaust manifold 20 and reduces the emissions levels of the exhaust gas.

A controller 30 communicates with various components of the engine control system 8, including but not limited to a throttle position sensor 32 (TPS), the fuel system 12, the ignition system 18, and a mass airflow sensor 36 (MAF). The controller 30 receives a throttle position signal from the TPS 32 and a mass air flow signal from the MAF 36. The throttle position signal and the mass air flow signal are used to determine air flow into the engine 14. The air flow data is then used to calculate the corresponding fuel to be delivered by the fuel system 12 to the engine 14. The controller 30 further communicates with the ignition system 18 to determine ignition spark timing. Oxygen sensors 46 and 48 are disposed in the exhaust 20 upstream and downstream, respectively, of the catalytic converter 22. The oxygen sensors 46 and 48 output signals to the controller 30 that represent the oxygen content before and after the catalytic converter 22 in the exhaust 20.

The controller 30 may receive additional feedback from other components in the engine control system 8, including but not limited to coolant temperature from a coolant temperature sensor 50 and engine speed from the engine speed sensor 34 (RPM). These and other variables may affect the overall performance and behavior of the engine control system 8. The controller 30 utilizes data gathered from the various engine components to monitor and optimize engine performance.

With continued reference to FIG. 1 and further reference to FIG. 2, the controller 30 according to the present invention establishes a plurality of thresholds during closed loop fuel control to maintain optimum catalyst efficiency. The thresholds are defined as rich condition enable, rich condition disable, lean condition enable and lean condition disable. The control method is active only when normal closed loop fuel control conditions are met. The control method is inactive during other open loop fuel control or intrusive diagnostic modes. The controller 30 receives the oxygen signal generated by the downstream oxygen sensor 48. Based on the signal from the oxygen sensor 48, the controller 30 determines whether the established enable thresholds have been exceeded. For example, if the downstream oxygen sensor 48 generates a voltage signal below a predetermined threshold 70, control will enter an open loop rich control strategy. The open loop rich control strategy includes delivering an increased amount of fuel to the engine 14. An increased amount of fuel is delivered to return the downstream oxygen sensor 48 to a desired window 68. For example, increasing the amount of fuel delivered to the engine 14 may include increasing the fuel injection duration. The desired window 68 is defined as a predetermined optimum range of oxygen measured by the downstream oxygen sensor 48. The open loop rich control continues until accumulated airflow reaches its predetermined value or until a lean condition disable threshold 72 is met.

Similarly, if the downstream oxygen sensor 48 generates a voltage signal above a predetermined threshold 60, control will enter an open loop lean control strategy. The open loop lean control strategy includes delivering a reduced amount of fuel to the engine 14. A reduced amount of fuel is desired to return the downstream oxygen sensor 48 to the desired window 68. For example, decreasing the amount of fuel delivered to the engine 14 may include decreasing the fuel injection duration. The open loop lean control continues for a predetermined accumulated airflow or until a rich condition disable threshold 62 is met.

Referring now to FIG. 3, steps for optimizing fuel control in an internal combustion engine are shown generally at 100. Control begins with step 102. In step 104, control determines whether any applicable active faults are identified. The applicable active faults are those that may prevent the control from correct performance. Active faults may include component diagnostic trouble codes such as catalytic converter fault codes, oxygen sensor fault codes, cylinder misfire codes, and secondary fuel trim fault codes, etc. If one or more active fault codes are identified in step 104, control returns in step 124. If no active faults are identified in step 104, control determines whether the downstream oxygen sensor 48 is ready to support closed loop operation in step 108. If the oxygen sensor 48 is not ready to support closed loop operation, control returns in step 124. If the oxygen sensor 48 is ready, control determines whether other open loop fuel or intrusive diagnostic modes having higher priority are active in step 112.

If other open loop fuel or intrusive diagnostic modes are active, control returns in step 124. If there are no other open loop fuel or intrusive diagnostic modes active, control determines whether the engine 14 is operating correctly in closed loop mode in step 118. If the closed loop operation conditions are not met, control returns in step 124. If all the entire enable conditions are true, control runs a correction routine in step 120.

With reference now to FIG. 4, the correction routine 120 will be described in greater detail. The correction routine 120, as previously described, implements a brief open loop rich or lean control if the oxygen sensor 48 communicates a signal exceeding the enable conditions 60 or 70 (FIG. 2). The correction routine 120 begins in step 140. In step 144, control determines if the oxygen sensor signal 48 has dropped below the lean condition enable threshold 70 or if the signal has exceeded the rich condition enable threshold 60 in step 148.

If the oxygen sensor signal 48 is below the lean condition enable threshold 70 in step 144, then an intrusive air/fuel ratio (AFR) control is implemented in step 150 having a rich fuel mixture of air/fuel (a ratio less than 14.7 to 1 for gasoline). An accumulated engine airflow variable is also set to zero in step 150 upon initiation of intrusive AFR control. In step 152 control determines if the oxygen sensor 48 communicates a signal satisfying the lean condition disable threshold 72. If the oxygen sensor 48 communicates a signal satisfying the lean condition disable threshold 72, control returns to normal closed loop control mode in step 156 and control returns in step 158. If the lean condition disable threshold 72 is not satisfied in step 152, control determines if intrusive AFR control has been running beyond one or more predetermined applicable criteria in step 160. The applicable criteria can be an accumulated airflow, lapsed time or other variables. For an example, the accumulated airflow is used for demonstration. If the AFR control has exceeded the predetermined accumulated engine airflow calibration in step 160, control returns to normal closed loop control mode in step 156 and control returns in step 158. If the AFR control has not exceeded the calibration, the accumulated engine airflow is incremented in step 164 and control loops to step 152.

In step 148, control determines whether the oxygen sensor 48 communicates a signal exceeding the rich condition enable threshold 60. If the rich condition enable threshold 60 is not exceeded in step 148, control returns to normal closed loop control in step 156 and control returns in step 158.

If the rich condition enable threshold 60 is exceeded in step 148, an intrusive air/fuel ratio (AFR) control is implemented in step 170 having a lean fuel mixture of air/fuel (a ratio greater than 14.7 to 1 for gasoline). An accumulated engine airflow variable is also set to zero in step 170 upon initiation of intrusive AFR control. In step 172, control determines whether the oxygen sensor 48 communicates a signal satisfying the rich condition disable threshold 62. If the oxygen sensor 48 communicates a signal satisfying the rich condition disable threshold 62, control returns to normal closed loop control mode in step 156 and control returns in step 158. If the rich condition disable threshold 62 is not satisfied in step 172, control determines whether intrusive AFR control has been running beyond one or more predetermined applicable criteria in step 180. The applicable criteria can be an accumulated airflow, lapsed time or other variables. For an example, the accumulated airflow is used for demonstration. If the AFR control has exceeded the predetermined accumulated engine airflow calibration in step 180, control returns to normal closed loop control mode in step 156 and control returns in step 158. If the AFR control has not exceeded the calibration, the accumulated engine airflow is incremented in step 184 and control loops to step 172.

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims. 

1. A control system for optimizing fuel control in an internal combustion engine, comprising: an exhaust connected to said engine and having a catalytic converter disposed therein; an oxygen sensor disposed in said exhaust downstream of said catalytic converter that generates an oxygen signal; and a controller that communicates with said oxygen sensor and that modifies an air/fuel mixture introduced into said engine based on said oxygen signal from said oxygen sensor.
 2. The control system of claim 1 wherein said controller compares said signal to a predetermined lean condition enable threshold that represents an oxygen content that is greater than desired, and wherein said controller introduces an increased amount of fuel into said engine based on said signal dropping below said predetermined lean condition enable threshold.
 3. The control system of claim 1 wherein said controller compares said signal to a predetermined rich condition enable threshold that represents an oxygen content that is less than desired, and wherein said controller introduces a reduced amount of fuel into said engine based on said signal exceeding said predetermined rich condition enable threshold.
 4. The control system of claim 2 wherein said controller compares said signal to a predetermined lean condition disable threshold that represents an oxygen content that is greater than a desired level, but appropriate to return to normal closed loop fueling, and wherein said controller returns fuel delivery to a normal operation based on said signal satisfying said lean condition disable threshold.
 5. The control system of claim 3 wherein said controller compares said signal to a predetermined rich condition disable threshold that represents an oxygen content that is less than a desired level, but appropriate to return to normal closed loop fueling, and wherein said controller returns fuel delivery to a normal operation based on said signal satisfying said rich condition disable threshold.
 6. The control system of claim 2 wherein said controller initiates an accumulated engine airflow variable and concludes introducing increased amounts of fuel to said engine based on said accumulated engine airflow reaching a predetermined condition.
 7. The control system of claim 3 wherein said controller initiates an accumulated engine airflow variable and concludes introducing reduced amounts of fuel to said engine based on said accumulated engine airflow reaching a predetermined condition.
 8. A method for optimizing fuel control in an internal combustion engine, comprising: utilizing a signal from an oxygen sensor disposed in an exhaust downstream of a catalytic converter; determining whether said signal exceeds predetermined thresholds; compensating an air/fuel mixture introduced into the engine based on said signal exceeding said predetermined thresholds.
 9. The method of claim 8 wherein determining if said signal exceeds predetermined thresholds comprises: comparing said signal to a predetermined lean condition enable threshold that represents an oxygen content that is greater than desired; and introducing an increased amount of fuel into said engine based on said signal dropping below said predetermined lean condition enable threshold.
 10. The method of claim 8 wherein determining if said signal exceeds predetermined thresholds comprises: comparing said signal to a predetermined rich condition enable threshold that represents an oxygen content less than desired; and introducing a reduced amount of fuel into said engine based on said signal exceeding said predetermined rich condition enable threshold.
 11. The method of claim 9, further comprising: comparing said signal to a predetermined lean condition disable threshold that represents an oxygen content greater than a desired level, but appropriate for the return to normal closed loop fueling; and returning fuel delivery to a normal operation based on said signal satisfying said lean condition disable threshold.
 12. The method of claim 10, further comprising: comparing said signal to a predetermined rich condition disable threshold that represents an oxygen content less than a desired level, but appropriate for the return to normal closed loop fueling; and returning fuel delivery to a normal operation based on said signal satisfying said rich condition disable threshold.
 13. The method of claim 9, wherein introducing an increased amount of fuel comprises introducing an increased amount of fuel into said engine for a predetermined maximum accumulated airflow.
 14. The method of claim 10, wherein introducing a reduced amount of fuel further comprises introducing a reduced amount of fuel into said engine for a predetermined maximum accumulated airflow.
 15. A method for optimizing fuel control in an internal combustion engine comprising: determining whether said engine is operating in closed loop control; utilizing a signal from an oxygen sensor disposed in an exhaust system downstream of a catalytic converter; determining if said signal exceeds predetermined thresholds; and introducing a modified amount of fuel into said engine based on said signal exceeding said predetermined thresholds.
 16. The method of claim 15 wherein determining if said engine is meeting closed loop control conditions further comprises: determining whether diagnostic trouble codes are inactive; and determining whether said oxygen sensor has reached operating temperature and been ready for use; and determining whether other open loop fueling or intrusive diagnostic modes are inactive.
 17. The method of claim 15 wherein determining if said signal exceeds predetermined thresholds comprises: comparing said signal to a predetermined lean condition enable threshold that represents an oxygen content greater than desired; and introducing an increased amount of fuel into said engine based on said signal below said predetermined lean condition enable threshold.
 18. The method of claim 15 wherein determining if said signal exceeds predetermined thresholds comprises: comparing said signal to a predetermined rich condition enable threshold that represents an oxygen content less than desired; and introducing a reduced amount of fuel into said engine based on said signal above said predetermined rich condition enable threshold.
 19. The method of claim 17, further comprising: comparing said signal to a predetermined lean condition disable threshold that represents an oxygen content greater than a desired level, but appropriate for the return to normal closed loop fueling; and returning fuel delivery to a normal operation based on said signal satisfying said lean condition disable threshold.
 20. The method of claim 18, further comprising: comparing said signal to a predetermined rich condition disable threshold that represents an oxygen content less than a desired level, but appropriate for the return to normal closed loop fueling; and returning fuel delivery to a normal operation based on said signal satisfying said rich condition disable threshold. 